Vented lead blade

ABSTRACT

A vented lead blade for use in a paper making machine located so that the stock jet impinges the forming fabric at, or near to, its trailing edge. The vented lead blade serves to bend the forming fabric before it enters the forming section, and to vent at least a substantial proportion of any air which becomes trapped in the wedge shaped space between the surface of the forming fabric and the surface of the stock jet, together with at least some of any liquid carried with the air. The vented lead blade of this invention thus enables the forming fabric to be positioned so that the angle of impingement of the stock jet onto the forming fabric can be minimized to become substantially zero. It also makes it possible to reduce the unsupported length of the stock jet. The vented lead blade of this invention can be used in both an open surface forming section with one forming fabric, or in the forming section of a two fabric paper making machine.

FIELD OF THE INVENTION

[0001] This invention concerns a vented lead blade for use in a papermaking machine.

BACKGROUND OF THE INVENTION

[0002] In the initial portion of the forming section of either a singleor two fabric papermaking machine, an unsupported jet of highly aqueousstock is ejected from the head box slice onto the surface of a movingforming fabric. The unsupported jet will typically traverse a distanceof from about 6 cm to about 40 cm before impinging the surface of theforming fabric at the point of impingement. The angle of impingement, α,formed between the stock jet and the plane of the forming fabric at thepoint of impingement will typically be from about 40° to about 10°. Itis well known that improved paper formation can be obtained byminimizing both the angle a and the length of the unsupported free jet.

[0003] As the angle α increases, the magnitude of the pressure exertedby the jet on the surface of the forming fabric also increases.

[0004] For a forming fabric moving at a speed of 20 m/sec and a jet ofpure water, the impingement pressure I in kPa can be shown to be givenby the following relationship:

I=200 sin α.

[0005] Typical peak impingement pressures for different values of theangle a are shown in Table 1. TABLE 1 Peak Impingement Pressure Angle ofImpingement, α° Pressure (I, kPa) 1 3.49 2 6.98 4 13.95 6 20.90 8 27.8310  34.73

[0006] Impingement angles greater than about 5° will create peakimpingement pressures that may cause sheet marking, low retention ofpaper making fines and fillers, and plugging of the forming fabric.Therefore, the angle α should be made as small as possible so that,ideally, the unsupported stock jet impinges on the fabric substantiallytangentially.

[0007] As the length of the stock jet increases, its outside surfacebegins to break up into ridges and furrows, which will eventually causesheet basis weight variations. Further, finely dispersed fibers in thestock start to reflocculate rapidly in the unsupported jet prior to thepoint of impingement. Therefore, the unsupported stock jet should bemade as short as possible to minimize these effects.

[0008] Due to the competing space requirements of both the head boxslice lip structure and the adjacent upstream rolls such as a breastroll, it is difficult to shorten the unsupported stock jet lengthwithout increasing the angle α. Even if the head box slice lips can belocated so that the angle a is very small, and the free jet is nearlytangential to the forming fabric, air that is trapped in the small wedgeshaped space between the surface of the forming fabric and the surfaceof the unsupported stock jet becomes entrained into the stock formingbubbles which are detrimental to sheet formation.

[0009] Several proposals have been made to overcome these difficulties.Nelson et al, U.S. Pat. No. 3,440,136 discloses a method of avoiding airentrainment by evacuating the air from the forming zone, and floodingthis area with water. However this proposal has been found to bedifficult to realize in practice. Irwin et al., U.S. Pat. No. 4,734,164,disclose a forming board for a single fabric machine in which the firstblade is slightly curved to permit the breast roll to be loweredslightly. The difficulty with this proposal is that air is trapped inthe shallow wedge space between the jet and the forming fabric as itpasses over the curved first blade. This air is forced into the stock asbubbles which cause formation defects. Malashenko, U.S. Pat. No.4,802,954, discloses a lead-in blade located ahead of the curved bladeelement proposed by Irwin et al., which is said to reduce the amount offluid pumped by the forming fabric into the wedge shaped space betweenthe jet and the fabric. However, a small wedge shaped air space remains.The pressure in this space is controlled by a vacuum pump to reduce thejet disturbance. Ewald in U.S. Pat. No. 5,084,138 addresses the problemof excessive free jet length by using curved turning bars to replacelarge diameter breast rolls and a solid curved blade, but does not avoidair entrapment at the wedge between the jet and the fabric.

[0010] The present invention seeks to provide a lead blade for use inthe forming shoe or forming board of a high speed paper making machinewhich will eliminate or at least substantially reduce all of theaforementioned deficiencies of the prior art by means of a constructionand arrangement which at least in part adopts these recommendations.

SUMMARY OF THE INVENTION

[0011] This invention seeks to provide a vented lead blade for usedownstream of the breast roll, between the breast roll and the fabricsupporting elements in the forming section, and located so that thestock jet impinges the forming fabric at, or near to, its trailing edge.The vented lead blade does two things. First, it serves to bend theforming fabric before it enters the forming section. Second, it servesto vent at least a substantial proportion of any air which becomestrapped in the wedge shaped space between the surface of the formingfabric and the surface of the stock jet. The vented lead blade of thisinvention thus enables the forming fabric to be positioned so that theangle α can be minimized, and, if desired, by allowing the breast rollto be repositioned to create space into which the head box can be moved,thus reducing the unsupported length of the stock jet. The vented leadblade of this invention can be used in both an open surface formingsection with one forming fabric, or in the forming zone of a two fabricpaper making machine.

[0012] Thus in a first broad embodiment this invention seeks to providea curved vented lead blade for use in a paper making machine upstreamof, and immediately adjacent to, the point of impingement of a stock jetejected from a head box slice onto a moving forming fabric carrying anamount of liquid, which lead blade has a leading edge, a shaped trailingedge portion, including a trailing edge, and a convexly curved surfacelocated between the leading edge and the trailing edge portion, overwhich the forming fabric moves in sliding contact and wraps through anangle of wrap θ, the convexly curved surface and the trailing edgeportion including a plurality of grooves which begin at the leading edgeand end at the trailing edge constructed and arranged to vent at thelead blade trailing edge at least a substantial proportion of any airtrapped in the forming fabric from a wedge shaped space between thestock jet and the forming fabric surface, and at least some of theliquid carried by the forming fabric.

[0013] In a second broad embodiment this invention seeks to provide apapermaking machine, having a machine direction and a cross machinedirection, which includes:

[0014] a forming fabric moving in the machine direction;

[0015] a head box including a head box slice which provides a jet ofpaper making stock which impinges at an angle of impingement onto theforming fabric at a point of impingement;

[0016] a roll, having a cylindrical surface whose axis is in the crossmachine direction, about which the forming fabric passes, and which islocated upstream of the head box slice;

[0017] a forming section, located downstream of the point ofimpingement, including static support elements which define a fabricpath through which the forming fabric passes; and

[0018] a vented lead blade, located upstream of, and immediatelyadjacent to, the point of impingement of a stock jet ejected from a headbox slice onto a moving forming fabric, about which a forming fabricwraps through a wrap angle θ;

[0019] wherein the vented lead blade has a leading edge, a shapedtrailing edge portion including a trailing edge and a convexly curvedsurface, located between the leading edge and the trailing edge portion,over which the forming fabric moves in sliding contact and wraps throughan angle of wrap θ, the convexly curved surface and the trailing edgeportion including a plurality of grooves which begin at the leading edgeand end at the trailing edge constructed and arranged to vent at thelead blade trailing edge at least a substantial proportion of any airtrapped in the forming fabric from a wedge shaped space between thestock jet and the lead blade curved surface, and at least some of theliquid carried by the forming fabric.

[0020] In a third broad embodiment this invention seeks to provide apapermaking machine, having a machine direction and a cross machinedirection, which includes:

[0021] a first and a second forming fabric each moving in the machinedirection;

[0022] a head box including a head box slice which provides a jet ofpaper making stock which impinges at an angle of impingement onto atleast one of the forming fabrics at a point of impingement;

[0023] two rolls, each having a cylindrical surface whose axis is in thecross machine direction, about each of which one of the forming fabricpasses, and which are located adjacent the head box slice;

[0024] a forming section, located downstream of the point ofimpingement, including static support elements which define a fabricpath through which the forming fabric passes; and

[0025] two vented lead blades, each located upstream of, and immediatelyadjacent to, the point of impingement of the stock jet, about the firstof which the first forming fabric wraps through a wrap angle θ₁, andabout the second of which the second forming fabric wraps through a wrapangle θ₂;

[0026] wherein each vented lead blade has a leading edge, a shapedtrailing edge portion including a trailing edge and a convexly curvedsurface, located between the leading edge and the trailing edge portion,over which the forming fabric moves in sliding contact and wraps throughan angle of wrap, the convexly curved surface and the trailing edgeportion including a plurality of grooves which begin at the leading edgeand end at the trailing edge constructed and arranged to vent at thelead blade trailing edge at least a substantial proportion of any airtrapped in the forming fabric from a wedge shaped space between thestock jet and the lead blade curved surface, and at least some of theliquid carried by the forming fabric.

[0027] Preferably, the convexly curved surface is essentially circular,with a constant radius. More preferably, the shaped trailing edgeportion conforms to the convexly curved surface. Alternatively, theconvexly curved surface is not circular, and the radius of curvatureincreases towards the trailing edge. Conveniently, the convexly curvedsurface is not circular, the radius of curvature increases towards thetrailing edge, and the shaped trailing edge portion is essentially flat.

[0028] Preferably, the convexly curved surface has an effective radiusof curvature that is from about 50% to about 100% of the radius of theadjacent upstream roll. The radius of curvature will not generally begreater than that of the adjacent upstream roll.

[0029] Preferably, the angle θ, θ₁ or θ₂ through which the formingfabric wraps the lead blade is from about 10° to about 40°. Morepreferably, the angle of wrap is from about 15° to about 300°. Mostpreferably, the angle of wrap is from about 20° to about 25°.

[0030] Preferably, in a paper making machine having two forming fabrics,the two vented lead blades are the same, and their convexly curvedsurfaces are the same shape. Alternatively, in a paper making machinehaving two forming fabrics, the two vented lead blades are not the same,and their convexly curved surfaces are not the same shape.

[0031] Preferably, in a paper making machine having two forming fabrics,the two vented lead blades are the same, the angles θ₁ and θ₂ are thesame, and their convexly curved surfaces are the same shape.Alternatively, in a paper making machine having two forming fabrics, thetwo vented lead blades are not the same, the angles θ₁ and θ₂ are notthe same, and their convexly curved surfaces are not the same shape.

[0032] The invention will now be described with reference to theattached schematic drawings in which:

[0033]FIG. 1 shows part of an open surface paper making machineincluding a vented lead blade;

[0034]FIGS. 2 and 3 show parts of two different twin fabric paper makingmachines;

[0035]FIGS. 4, 5 and 6 show the effects of wrap angle and vented leadblade effective radius;

[0036]FIGS. 7, 8 and 9 show three different groove arrangements for thevented lead blade top surface; and

[0037]FIG. 10 shows four different groove shapes.

[0038] In FIGS. 1-6 only the parts of the paper making machine requiredfor an understanding of this invention are shown.

[0039]FIG. 1 shows a paper making machine which includes a vented leadblade according to the teachings of this invention. The slice lips 1Aand 1B of the head box deliver a jet of stock 2 onto the forming fabric3 at the impingement point I. The forming fabric 3 passes around theroll 6, wraps the vented lead blade 5, and then passes over the firststatic support element 4 in the forming section. As the moving formingfabric 3 and the stock jet 2 converge, air 8 in the wedge shaped spacebetween the surface of the stock jet 9, the surface 10 of the head boxlip 1B, and the surface of the forming fabric 11 becomes trapped andenters the forming fabric 3. This air, together with some of the liquidin the forming fabric at this point, passes through the forming fabric 3into the grooves 12 in the top surface of the vented lead blade 5.

[0040] In this arrangement, since the axis 15 of the roll 6 is nowlocated out of the fabric path 7, and since the vented lead blade 5occupies far less space than the roll, it is possible to maintain theangle of impingement close to zero, and to shorten the unsupportedlength D of the stock jet 2 significantly. Further, since the trailingedge 14 of the vented lead blade 5 is closely adjacent the impingementpoint I, the trapped air is prevented from interfering in the formationprocess within the stock in the forming section. The grooves 12 arelocated and dimensioned so that at least a substantial proportion, andpreferably all, of the air passing through the forming fabric, togetherwith any liquid carried with the air from the liquid on the formingfabric at this point, is vented as at 13 from the vented lead blade atits trailing edge 14.

[0041]FIGS. 2 and 3 show a paper making machine which has two formingfabrics, and which incorporates two vented lead blades according to theteachings of this invention. In describing these two Figures the terms“upper” and “lower” refer only to the orientation shown: in practice ina twin fabric machine the forming section is often oriented vertically,or at some angle thereto.

[0042] Referring first to FIG. 2, the slice lips 1A and 1B deliver a jetof stock 2 onto the lower forming fabric 31 at the impingement point I.The forming fabric 31 wraps the lower vented lead blade 51. As themoving forming fabric 31 and the stock jet 2 converge, air 81 in thewedge shaped space between the surface of the stock jet 91, the surface101 of the head box lip 1B, and the surface of the forming fabric 111becomes trapped and enters the forming fabric 31. This air 81, togetherwith some of the liquid in the forming fabric 31 at this point, passesthrough the forming fabric 31 into the grooves 121 in the lower ventedlead blade 51. The accumulated air and liquid 131 is vented from thelower vented lead blade 51 at its trailing edge 141. The construction asregards the lower forming fabric 51 is thus essentially the same asFIG. 1. Downstream of the impingement point I a second forming fabric 32converges with the upper side 92 of the stock 2 on the lower formingfabric 31. Further air is trapped in the space 82 between the lower face112 of the upper forming fabric 32 and the surface 92 of the stock 2.This additional air, and some of the liquid in the forming fabric 52,passes through the forming fabric 52 into the grooves 122 and is ventedat the trailing edge 142 of the upper vented lead blade 52.

[0043]FIG. 3 shows an alternative arrangement to that of FIG. 2. Thearrangement of the lower forming fabric 31 is the same. The upperforming fabric 32 converges with the stock jet 2 at the same point asthe lower forming fabric 31, more or less at the impingement point I.For the upper forming fabric air is now trapped in the space bounded bythe upper surface 92 of the stock jet, the lower surface 112 of theupper forming fabric 32, and the upper surface 102 of the head box lip1A. All of the trapped air, together with some of the liquid in the twoforming fabrics, is vented through the grooves 121, 122 at the trailingedges 141, 142 of the two vented lead blades 51, 52.

[0044] In both of these twin fabric machines, the two vented lead bladeswill often be the same, and have the same convexly curved shape. Howeverin some circumstances it may be desirable to use two different ventedlead blades, which may have different convexly curved shapes. It is alsothen possible that the two wrap angles θ₁ and θ₂ will likely be similar,they may not be the same.

[0045]FIGS. 4, 5 and 6 show the relationship between the angle θ throughwhich the forming fabric 3 wraps about a vented lead blade, theeffective radius of curvature of the vented lead blade, and the radiusof the adjacent upstream roll. Each of these Figures uses the samenumbers as FIG. 1, and thus considers a single fabric machine. Similarconsiderations apply to a twin fabric machine.

[0046] In each of these Figures, the convexly curved surface 16 of thevented lead blade 5 has a constant radius, the forming fabric 3 isreceived tangentially from the adjacent upstream roll 6, and theimpingement point I is adjacent the trailing edge 14 of the vented leadblade 5. These three Figures are also shown to essentially the samescale.

[0047] In FIG. 4, the radius R₄ of the vented lead blade surface 16 isthe same as the radius R₁ of the roll 6, which is some distance from thehead box slice lips 1A, 1B. The vented lead blade 5 then has to berelatively wide in order to bend the forming fabric 3 into the formingpath 7. If R₁ and R₄ are both approximately 46 cm, the angle of wrap θ₄is about 18°. This large radius also implies that the length D₄ of theunsupported stock jet 2 cannot be shortened very much.

[0048] In FIG. 5, the radius R₅ of the vented lead blade surface 16 issmaller than the radius R₁ of the roll 6, which is still some distancefrom the head box slice lips 1A, 1B. The vented lead blade 5 then stillhas to be relatively wide in order to bend the forming fabric 3 into theforming path 7. If R₁ is approximately 46 cm, and R₅ is approximately 23cm, the angle of wrap θ₅ is about 36°. This smaller radius R₅ allows thelength D₅ of the unsupported stock jet 2 to be shortened.

[0049] In FIG. 6, the radius R₆ of the vented lead blade surface 16 issmaller than the radius R₁ of the roll 6, which is now closer to thehead box slice lips 1A, 1B. The vented lead blade 5 is much narrower inorder to bend the forming fabric 3 into the forming path 7. If R₁ isapproximately 46 cm, and R₆ is approximately 23 cm, the angle of wrap θ₆is about 18°. This smaller radius R₅ allows the length D₆ of theunsupported stock jet 2 to be shortened still further.

[0050] It can thus be seen that the vented lead blade of this inventionprovides considerable flexibility in the geometry of the machine wetend.

[0051] The curved surface of the lead in blade is vented by means ofgrooves which begin at the extreme upstream edge of the blade and arecontinuous to its downstream edge. Three groove arrangements are shownin FIGS. 7, 8 and 9. In each Figure, the forming fabric moves in thedirection of the arrow A. In FIG. 7, the grooves 17 are regularly spacedthe same distance apart, and are essentially parallel to the arrow A.The disadvantage with this arrangement is that there is some risk of theforming fabric tracking across the blade. This is avoided in FIG. 8,where although the grooves 18 are still regular and parallel, they areat an angle β to the arrow A. Alternatively, two sets of angled grooves18A, 18B can be used as shown in FIG. 9. Within each set, the groovesare parallel to each other and regularly spaced, and each set is at anangle β to the arrow A. Typically, the angle β in FIGS. 8 and 9 will befrom about 20 to about 300.

[0052] The purpose of the grooves in the vented lead blade surface is toprovide spaces through which at least a substantial proportion of theair is vented which enters the forming fabric from the wedge shapedspace essentially between the forming fabric and the jet surface. At thesame time, at least some of the liquid in the forming fabric as itenters the forming section will also be vented.

[0053]FIG. 10 shows four possible groove structures for this purpose.For simplicity, the blade surface 17 has been shown flat; in practice itwill be curved. Groove 19 is of constant width for its entire lengthfrom the leading edge 17A to the trailing edge 17B. As the fabric passesover the vented lead blade surface 17, air is continuously entering theforming fabric. It is thus often advantageous to use a groove with anincreasing cross section, such as the groove 20 which widens, or thegroove 21 which deepens, or the groove 22 which both widens and deepens,in each case from the leading edge 17A to the trailing edge 17B.Typically, the grooves 19, 20, 21 and 22 are from 2-8 mm in width, and1-8 mm in depth.

[0054] In operation, the forming fabric moves in sliding contact as itwraps the vented lead blade. At the point of contact of the formingfabric with the upstream leading edge of the lead blade, for example at17A in FIG. 10, the fabric may form a small contact angle that isideally 0.50 or less. It is preferred that the forming fabric istangential to the vented lead blade surface at this point. The leadingedge of the blade can be curved to minimize any frictional effects atthis point; a suitable edge radius is from about 0.0025 mm to about0.0065 mm. The forming fabric should exit the vented lead bladetangentially to the trailing edge portion of the blade surface,substantially in the path defined by the downstream fabric supportelements. The downstream path of the forming fabric should be parallelto and in the same plane as the underside of the stock jet, so that theangle of impingement of the stock jet onto the forming fabric issubstantially zero.

What is claimed is:
 1. A curved vented lead blade for use in a papermaking machine upstream of, and immediately adjacent to, the point ofimpingement of a stock jet ejected from a head box slice onto a movingforming fabric carrying an amount of liquid, which lead blade has aleading edge, a shaped trailing edge portion, including a trailing edge,and a convexly curved surface located between the leading edge and thetrailing edge portion, over which the forming fabric moves in slidingcontact and wraps through an angle of wrap θ, the convexly curvedsurface and the trailing edge portion including a plurality of grooveswhich begin at the leading edge and end at the trailing edge constructedand arranged to vent at the lead blade trailing edge at least asubstantial proportion of any air trapped in the forming fabric from awedge shaped space between the stock jet and the forming fabric surface,and at least some of the liquid carried by the forming fabric.
 2. Apapermaking machine, having a machine direction and a cross machinedirection, which includes: a forming fabric moving in the machinedirection; a head box including a head box slice which provides a jet ofpaper making stock which impinges at an angle of impingement onto theforming fabric at a point of impingement; a roll, having a cylindricalsurface whose axis is in the cross machine direction, about which theforming fabric passes, and which is located upstream of the head boxslice; a forming section, located downstream of the point ofimpingement, including static support elements which define a fabricpath through which the forming fabric passes; and a vented lead blade,located upstream of, and immediately adjacent to, the point ofimpingement of a stock jet ejected from a head box slice onto a movingforming fabric, about which a forming fabric wraps through a wrap angleθ; wherein the vented lead blade has a leading edge, a shaped trailingedge portion, including a trailing edge, and a convexly curved surfacelocated between the leading edge and the trailing edge portion, overwhich the forming fabric moves in sliding contact and wraps through anangle of wrap θ, the convexly curved surface and the trailing edgeportion including a plurality of grooves which begin at the leading edgeand end at the trailing edge constructed and arranged to vent at thelead blade trailing edge at least a substantial proportion of any airtrapped in the forming fabric from a wedge shaped space between thestock jet and the lead blade curved surface, and at least some of theliquid carried by the forming fabric.
 3. A papermaking machine, having amachine direction and a cross machine direction, which includes: a firstand a second forming fabric each moving in the machine direction; a headbox including a head box slice which provides a jet of paper makingstock which impinges at an angle of impingement onto at least one of theforming fabrics at a point of impingement; two rolls, each having acylindrical surface whose axis is in the cross machine direction, abouteach of which one of the forming fabric passes, and which are locatedadjacent the head box slice; a forming section, located downstream ofthe point of impingement, including static support elements which definea fabric path through which the forming fabric passes; and two ventedlead blades, each located upstream of, and immediately adjacent to, thepoint of impingement of the stock jet, about the first of which thefirst forming fabric wraps through a wrap angle θ₁, and about the secondof which the second forming fabric wraps through a wrap angle θ₂;wherein each vented lead blade has a leading edge, a shaped trailingedge portion, including a trailing edge, and a convexly curved surfacelocated between the leading edge and the trailing edge portion, overwhich the forming fabric moves in sliding contact and wraps through anangle of wrap, the convexly curved surface and the trailing edge portionincluding a plurality of grooves which begin at the leading edge and endat the trailing edge constructed and arranged to vent at the lead bladetrailing edge at least a substantial proportion of any air trapped inthe forming fabric from a wedge shaped space between the stock jet andthe lead blade curved surface, and at least some of the liquid carriedby the forming fabric.
 4. A curved vented lead blade according to claim1 wherein the convexly curved surface is essentially circular, with aconstant radius.
 5. A curved vented lead blade according to claim 1wherein the shaped trailing edge portion conforms to the convexly curvedsurface.
 6. A curved vented lead blade according to claim 1 wherein theconvexly curved surface is not circular, and the radius of curvatureincreases towards the trailing edge.
 7. A curved vented lead bladeaccording to claim 1 wherein the convexly curved surface is notcircular, the radius of curvature increases towards the trailing edge,and the shaped trailing edge portion is essentially flat.
 8. A curvedvented lead blade according to claim 1 wherein the convexly curvedsurface has an effective radius of curvature that is from about 50% toabout 100% of the radius of the adjacent upstream roll.
 9. A curvedvented lead blade according to claim 1 wherein the angle θ is from about10° to about 40°.
 10. A curved vented lead blade according to claim 9wherein the angle θ is from about 15° to about 30°.
 11. A curved ventedlead blade according to claim 10 wherein the angle θ is from about 20°to about 25°.
 12. A paper making machine according to claim 3 whereinthe two vented lead blades are the same, and their convexly curvedsurfaces are the same shape.
 13. A paper making machine according toclaim 3 wherein the two vented lead blades are not the same, and theirconvexly curved surfaces are not the same shape.
 14. A paper makingmachine according to claim 3 wherein the two vented lead blades are thesame, the angles θ₁ and θ₂ are the same, and the convexly curvedsurfaces are the same shape.
 15. A paper making machine according toclaim 3 wherein the two vented lead blades are not the same, the anglesθ₁ and θ₂ are not the same, and the two convexly curved surfaces are notthe same shape.
 16. A paper making machine according to claim 2including a vented lead blade according to claims 4, 5, 6, 7, 8, 9 or10.
 17. A paper making machine according to claim 3 including a firstvented lead blade according to claims 4, 5, 6, 7, 8, 9 or
 10. 18. Apaper making machine according to claim 3 including a second vented leadblade according to claims 4, 5, 6, 7, 8, 9 or 10.